c++ - redirection of ./a.out is not capturing segmentation fault

Question

I run the command

./a.out < in &> output.txt

I want the errors also to be placed in output.txt.
The exit status of the command was 139 and on terminal its output was:

Segmentation fault (core dumped)

and the file output.txt was empty.

Answer 1

The message Segmentation fault (core dumped) is not coming from your program.

It's produced by shell as result of a signal received by it. It's not a part of stderr or stdout of your program.

So shell's message can be captured as:

{ ./a.out; } 2> out_err